The present invention relates generally to a solvent vapour collector for use in conjunction with an oven for curing coatings containing vapourizable solvents as applied to strip sheet and especially strip sheet metal.
In such known coating/curing plants, the coating is applied to the strip sheet metal at a coating station, for example, by passage between coating rollers. From the coating station, the coated strip passes to the curing oven in which the coating is dried or cured with the vaporization of the solvent from the coating.
Most such solvents are hazardous and must be eliminated before oven gases are exhausted into the atmosphere. Additionally, many such solvents are oxidizable and can be oxidized either by incineration or catalytic oxidation to provide heat which can be utilized in the curing oven so reducing the amount of primary fuel required for oven operation.
Considerable attention has already been given to the treatment of the solvent vapours released in the oven and many systems have heretofore been proposed for incinerating such oven solvent fumes. However, some solvent fumes are released into the coating room atmosphere and so escape treatment; their heat values are lost and they present an environmental and occupational hazard.
It will be appreciated that solvent vapours will inevitably escape not only from the coating station itself but also from the coated strip during its passage from the coating station to the oven inlet. Such escape of solvent vapours into the coating room atmosphere is especially severe when the strip entering the coating station is at an elevated temperature as is the case, for example, when a finish coat is being applied to a strip which has already been coated with a prime coating, such as a rust-proofing coating, and cured and is still at an elevated temperature. In such a coating station, the primed strip entering that coating station may still be at a temperature as high as 200.degree. to 250.degree. F. and consequently coating solvent will be vaporized rapidly and in relatively large amounts at the coating station and between that station and the oven inlet.
Quenching to a lower temperature would assist in solving this problem but many prime coatings are water based and it is not possible, therefore, to cool the strip by water quenching, air quenching below too slow to be effective.
In a situation of the type described, it is necessary and, in most jurisdictions, mandatory to extract such solvent fumes from the coater room in order to eliminate the health hazard and to avoid the risk of explosion concomitant with the existence of high solvent vapour levels.
While it is possible to provide a separate ventilation system for extracting such solvent fumes from the coater room, the provision of such a system would be relatively expensive. In many existing operations, the existing coater room ventilation systems would not have adequate capacity for handling the extra quantities of solvent vapours involved in an operation of the type hereinbefore mentioned and, in such a case, the replacement or supplementation of such an existing ventilating system would also involve considerable cost.
In existing operations where a tandem system is employed with the application and curing first of a priming coat and the subsequent application and curing of a finish coat, the problem of solvent evaporation at the finish coating station and between that coating station and the finish coat oven places limits on the actual line speed for the entire operation.
Accordingly, it is a principal object of this invention to provide a solvent vapour collector for use in conjunction with a coating-curing system of the type in question and with which solvent vapours released at a coating station and between such a coating station and an oven inlet can be collected and then mixed with the oven gases for treatment and recovery of heat values and also thereby ensuring adequate ventilation of the coater room.
It is a further object of this invention to provide a solvent vapour collector which permits the operating line speed of many existing coating-curing systems to be increased while avoiding the potential hazards which would otherwise result from the escape of increased volumes of solvent vapours.
Another object of this invention is to provide a solvent vapour collector which is relatively simple but versatile in its construction and which is, therefore, relatively inexpensive to construct and install.
Other objects of the invention will become apparent as the description herein proceeds.